The present invention relates to a non-aqueous ball point pen ink and a ball point pen using the ink. Specifically, the present invention relates to a non-aqueous ink provided with pseudoplasticity. The ink is provided by blending a non-Newtonian viscosity imparting agent while applying a cohesive force by blending a thickening agent comprising polyvinyl pyrrolidone with a weight-average molecular weight of about 40,000 to 100,000 to eliminate ink blobbing and scratching. The present also related to a non-aqueous ball point pen using this ink.
A conventional non-aqueous ball point pen has been designed by setting an ink viscosity in a range of 10,000 to 30,000 mPaxe2x80xa2s at 20xc2x0 C. to prevent leakage. However, when the viscosity during writing is high in this manner, the ball rotation resistance during writing automatically increases and writing smoothness is very low and fails to be satisfactory. Moreover, a high writing pressure is necessary during writing. In some cases, a load of 500 gf or more is applied to a pen point. The heavy load causes the pen point to be quickly damaged. Furthermore, ball breakage and writing defects frequently occur as a consequence. On the other hand, as disclosed in Japanese Patent Application Laid-Open Nos. 6-313143 (1994), 6-313144 (1994), 7-196972 (1995) and 9-48941 (1997), attempts were carried out to improve the above-described defects by creating inks having a pseudoplasticity viscosity property, where the ink viscosity during writing is low and where the ink viscosity is relatively high when writing is not performed. However, the but the attempts were not sufficient in enhancing the writing smoothness and completely preventing the leakage.
The present invention provides an ink which realizes a remarkably satisfactory writing smoothness, can be untilized for low pressure writing such as in conjunction with an aqueous ball point pen, forms a fresh drawn line, eliminates blobbing and feathering, and can completely prevent leakage. The present invention further provides a non-aqueous ball point pen in which no ink adheres to an ink reserving tube inner wall and an ink residual amount is clear.
The present invention relates to a non-aqueous ball point pen ink or ink composition in which a colorant, an organic solvent, a non-Newtonian viscosity imparting agent, and a thickening agent comprising only polyvinyl pyrrolidone with a weight-average molecular weight of about 40,000 to 100,000 are contained as main components. A non-Newtonian viscosity index of the ink may be as low as 0.1 and less than 0.4. The viscosity of the ink a shearing speed of 500 secxe2x88x921 may be as low as 1,000 and less than 3,000 mPaxe2x80xa2s at 20xc2x0 C. The viscosity of the ink in the shearing speed of 0.19 secxe2x88x921 may be as low as 40,000 mPaxe2x80xa2s at 20xc2x0 C. and as high as 70,000 mPaxe2x80xa2s at 20xc2x0 C. The non-aqueous ball point pen ink of this invention may contain polyvinyl pyrrolidone with the weight-average molecular weight of about 40,000 to 100,000 in a range of 1 to 3 mass % with respect to a total amount of the ink composition. The non-Newtonian viscosity imparting agent may be a fatty acid amide wax with a melting temperature of 140xc2x0 C. or more, and the content may be in a range of 2 to 5 mass % with respect to the total amount of the ink composition.
The ink may be directly filled into an ink reserving tube of a ball point pen. The ink reserving tube of the ball point pen may be a polypropylene tube with silicone applied to an inner face.
Various measures for enhancing a ball point pen stroke have been studied. Above all, it is a known fact that a ball rotation resistance exerts a remarkably large influence on the stroke, and it is also obvious that the ball rotation resistance depends on ink viscosity. Specifically, in order to enhance the stroke, it is a most effective measure to set the ink viscosity during writing to be as low as possible and reduce the ball rotation resistance. However, when the ink viscosity is set to be excessively low, problems such as leakage and blobbing, non-uniform line darkening (xe2x80x9cscratchingxe2x80x9d) and blurring (xe2x80x9cfeatheringxe2x80x9d) due to absorption by paper, etc. naturally increase. As described above, the technique of setting pseudoplasticity as an ink viscosity property to solve these problems has been disclosed, but the writing with a remarkably low pressure like an aqueous ball point pen and smooth sroke have not been realized, and a fresh drawn line has not been obtained.
Concretely, in order to enable the writing with the remarkably low pressure like the aqueous ball point pen, realize the smooth stroke and obtain the fresh drawn line, the ink viscosity during writing should preferably be less than 3,000 mPaxe2x80xa2s. In the present invention, a non-aqueous ink has been studied based on the prerequisite to invent a non-aqueous ball point pen ink which prevents leakage and blobbing, further scratching, and feathering from occurring, provides a superior touch, obtains a satisfactory drawn line and which causes no leakage. The blobbing means a phenomenon in which surplus ink during writing is accumulated in a pen point.
In the present invention, the viscosity in a shearing speed of 500 secxe2x88x921 may be as low as 1,000 and less than 3,000 mPaxe2x80xa2s at 20xc2x0 C., even though ink outside of this range is still acceptable. This is a viscosity area essential for realizing a remarkably smooth stroke, and obtaining a fresh drawn line like the aqueous ball point pen. With the viscosity less than 1,000 mPaxe2x80xa2s, the problem of feathering cannot be effectively prevented. Moreover, no satisfactory oil film can be formed between a ball and a ball seat and the intrinsic smoothness of the non-aqueous ball point pen can be deteriorated. On the other hand, with the viscosity of 3,000 mPaxe2x80xa2s or more, it is difficult to obtain a fresh drawn line relative to that obtained by an aqueous ball point pen. Specifically, in order to obtain a satisfactory stroke, the ink viscosity in the shearing speed of 500 secxe2x88x921 should preferably be set substantially to 10,000 mPaxe2x80xa2s or less. However, when the viscosity is 3,000 mPaxe2x80xa2s or more, a complete transfer type ball point pen, that is, a writing system of transferring the ink to a paper surface only via the ball can be constituted, the penetration to paper is reduced because of the high viscosity and no fresh drawn line can therefore be obtained.
According to experiments by the inventors of the present invention, when the ink viscosity in the shearing speed of 500 secxe2x88x921 is less than 3,000 mPaxe2x80xa2s, a writing utensil also utilizing the penetration to the paper surface can be obtained and a very fresh drawn line can be obtained. The ink viscosity described herein is measured in a measurement environment of 20xc2x0 C. using a rheometer CSL manufactured by British Carrymay, Ltd.
The most important constituting requirement in the present invention lies in that the ink viscosity in the shearing speed of 500 secxe2x88x921 is set as low as 1,000 and less than 3,000 mPaxe2x80xa2s at 20xc2x0 C., a non-Newtonian viscosity index is set as low as 0.1 and less than 0.4, remarkably low, the viscosity in the shearing speed of 0.19 secxe2x88x921 is further set to 40,000 mPaxe2x80xa2s (at 20xc2x0 C.) or more, and the ink is provided with pseudoplasticity. The necessity for setting the ink viscosity during writing to be low has been described above, but in this viscosity area, the leakage and blobbing, further scratching, and feathering could be increased. In order to prevent these defects, the necessity of setting the non-Newtonian viscosity index as low as 0.1 and less than 0.4 and setting the viscosity in the shearing speed of 0.19 secxe2x88x921 to 40,000 mPaxe2x80xa2s at 20xc2x0 C. or more arises. In other words, the above-described defects can be prevented by setting the pseudoplasticity as the ink viscosity property to be strong and setting the ink viscosity to be high during low shearing, that is, when not writing with the ball point pen. Additionally, when the ink viscosity exceeds 70,000 mPaxe2x80xa2s (at 20xc2x0 C.), ink fluidity can be lowered, ink follow-up property during writing can be deteriorated, and the inappropriate writing ink therefore preferably has to be avoided.
When the non-Newtonian viscosity index is less than 0.1, the pseudoplasticity can be excessively strong, and the ink follow-up defect may arise. In general, when the non-Newtonian viscosity index is less than 0.4, the cohesive force of the ink itself can become excessively strong and the ink follow-up defect may arise. However, when the ink viscosity in the shearing speed of 500 secxe2x88x921 is less than 3,000 mPaxe2x80xa2s, no channel resistance can be generated in a chip tip end as the thinnest part of an ink passage and no ink follow-up defect arises. On the other hand, when the non-Newtonian viscosity index is 0.4 or more, the pseudoplasticity increases. When the ink viscosity in the shearing speed of 500 secxe2x88x921 is set to no less than 1,000 and less than 3,000 mPaxe2x80xa2s (at 20xc2x0 C.), the leakage and blobbing, further scratching, and feathering cannot be prevented.
Furthermore, in order to thoroughly prevent the leakage, the viscosity in the shearing speed of 0.19 secxe2x88x921 should be 40,000 mPaxe2x80xa2s at 20xc2x0 C. When it is less than 40,000 mPaxe2x80xa2s, the leakage cannot completely be prevented.
The non-Newtonian viscosity imparting agent for use in the non-aqueous ink includes a fatty acid amide wax and a derivative thereof, linear chain fatty acid ester polymer, polyethylene oxide, hardened castor oil, organic bentonite, silica, sulfate-based anion activator, and the like, but the fatty acid amide wax is preferable based on stability. Further, considering the stability during the high-temperature preservation of the ball point pen, it is most preferable to select the fatty acid amide wax with a melting temperature of 140xc2x0 C. or more as the non-Newtonian viscosity imparting agent. The addition amount of the fatty acid amide wax varies with other blend amounts, but can be substantially in a range of 2.0 to 5.0 mass % in order to realize the non-Newtonian viscosity index of no less than 0.1 and less than 0.4.
The non-Newtonian viscosity index described herein is measured using the rheometer CSL manufactured by British Carrymay, Ltd., in a measurement environment of 20xc2x0 C. with appropriate values of angle and diameter of a cone plate in a shearing speed range of 1 to 600 secxe2x88x921.
The essential requirement of the present invention lies in that a colorant, an organic solvent, a non-Newtonian viscosity imparting agent, and a thickening agent comprising only polyvinyl pyrrolidone with a weight-average molecular weight of, preferably, 40,000 to 100,000 are contained as main components, and to obtain a satisfactory touch and fresh drawn line, the ink viscosity in the shearing speed of 500 secxe2x88x921 should preferably be set to no less than 1,000 and less than 3,000 mPaxe2x80xa2s at 20xc2x0 C.
Additionally, in general, in order to prevent the blobbing, a measure of employing polyvinyl pyrrolidone with a preferable weight-average molecular weight of 1,000,000 to 3,000,000 is used. This is actually a remarkably effective measure when the ink viscosity in the shearing speed of 500 secxe2x88x921 is 3,000 mPaxe2x80xa2s or more, but with the low viscosity of less than 3,000 mPaxe2x80xa2s as in the present invention, the effect is little, and the scratching is increased in vain. To describe that further, for polyvinyl pyrrolidone with the weight-average molecular weight of 40,000 to 100,000, the ball wetting with the ink is satisfactory in the pen point, and the scratching and line skipping are effectively prevented. Specifically, when the ink viscosity in the shearing speed of 500 secxe2x88x921 is not less than 1,000 and less than 3,000 mPaxe2x80xa2s (at 20xc2x0 C.), the satisfactory drawn line cannot be formed with the thickening agent other than polyvinyl pyrrolidone with the weight-average molecular weight of 40,000 to 100,000.
As polyvinyl pyrrolidone with the weight-average molecular weight of about 40,000 to 100,000, PVP K-30 (manufactured by GAF, Ltd., weight-average molecular weight of 55,000) is exemplified. The blend amount in the ink is preferably in a range of 1 to 3 mass % with respect to the total composition. With the amount less than 1 mass % there is a problem that the scratching cannot sufficiently be prevented, and conversely scratching easily arises with the amount exceeding 3 mass %.
The present inventors set the ink viscosity in the shearing speed of 500 secxe2x88x921 to no less than 1,000 and less than 3,000 mPaxe2x80xa2s at 20xc2x0 C. in order to realize a satisfactory touch and to obtain a fresh drawn line like the aqueous ball point pen ink. Moreover, the non-Newtonian viscosity index was set as low as 0.1 and less than 0.4, remarkably low, and the viscosity in the shearing speed of 0.19 secxe2x88x921 was set to 40,000 mpa.s or more, so that the contribution to prevention of the blobbing, leakage and feathering was made. Furthermore, scratching was prevented by using only polyvinyl pyrrolidone with the weight-average molecular weight of 4 to 50,000 as the thickening agent component. Specifically, the combination of these requirements is indispensable, and important because the target cannot be achieved when even one of them is lacking.
Other main components of the present invention will additionally be described. The colorant can be used without being particularly limited to the conventional dye or pigment employed in the non-aqueous ball point pen. Examples of the pigment include organic, inorganic and processed pigments, such as carbon black, phthalocyanine, azo, quinacridone, anthraquinone, and indigo pigments. Moreover, as the dye, an alcohol-soluble dye, oil-soluble dye, direct dye, acid dye, basic dye, metallized dye, and various salt-forming type dyes can be employed. Moreover, these can be used alone or as a mixture. The blend proportion is in a range of 5 to 50 mass %, preferably 20 to 40 mass % with respect to the total ink composition.
The organic solvent for use in the present invention is used as an ink composition solvent or dispersing medium. Concretely, alcohol and glycol solvents such as benzyl alcohol, propylene glycol and butylene glycol, Cellosolve solvents such as phenyl CELLOSOLVE, CARBITOL solvents such as phenyl CARBITOL, and nitrogen-containing solvents such as N-methyl pyrrolidone can be used alone or as a mixture. The blend proportion is preferably in a range of 30 to 70 mass % with respect to the total ink composition.
Here, a ball point pen structure will be described. For an ink reserving tube for the non-aqueous ball point pen, usable materials are limited from the standpoints of chemical resistance, moisture permeability, air permeability, and the like. In this respect, it has heretofore been most general to use polypropylene as the material. However, in the present invention particularly when the fatty acid amide wax is selected as the non-Newtonian viscosity imparting agent, the fatty acid amide wax has a very strong affinity for polypropylene. Therefore, as the ink is transferred from the ink reserving tube, a defect is generated that the ink adheres to the inner wall and the ink residual amount fails to be clarified. As a countermeasure against the defect, the present inventor et al. have found that when the ink reserving tube is formed of polypropylene, the ink reserving tube inner wall is to be treated with silicone. When silicone is applied to the ink reserving tube inner wall, polypropylene as the reserving tube material does not directly contact the ink and keeps a relation that silicone is interposed, so that during the movement of the ink, the prevention of adherence to the reserving tube inner wall is embodied. As a silicone material, TSF-4420 (Toshiba Silicone Co., Ltd.) is exemplified. It is a most effective application method to simultaneously and uniformly apply silicone to the inner wall during extrusion molding.
When a tube of polyethylene terephthalate or nylon is used as the ink reserving tube, the application of silicone is not necessarily required.